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Building An Oven

Started by D L Bahler, February 28, 2017, 12:26:31 PM

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D L Bahler

Started working on the body of the oven this evening, laid up one of the outside walls (because I won't be able to access it once the oven is built due to its closeness to the cabin) and went ahead and used up the rest of the mortar I had mixed up while I was at it.

Then I dry laid the bricks for the walls of the oven chamber itself.

You can see form of the oven starting to take shape. There is about 4 1/2 inches along the sides between the oven chamber bricks and the bricks of the out er wall. The next step is going to be to fill this area with sand to insulate the oven and also buttress the oven walls. The arches, also dry laid, will lay on top of the walls, and will naturally want to press outward. The arches need the added strength of the sand and the mortared outer walls to keep from toppling over. There will also be steel plates on the sides of the oven connected with reinforcing bars that pass through the structure just above the top of the oven chamber to help hold the walls against spreading.

Before I fill the void with sand, I'm going to render the outside of the dry laid bricks with mud (not clay, just ordinary mud) This makes it a little stronger, and helps with the thermal properties quite a bit.

The actual chamber ended up a little larger than the preliminary design, as a consequence of the size of the bricks. The basic plan was 4x8, but the actual intention was to make it whatever the size of the bricks dictated nearest those dimensions. I wanted to do as little cutting as possible.



  

  

  

  

  

  

  

 

So now the agenda looks like:

-Render the outside of the oven chamber walls with mud
-Finish laying up the outer structural walls
-Fill the voids with sand
-Lay up the arches
-Attach reinforcing rods and plates to structure while laying the arches.
-Render the top of the arch with mud.
-Build the exhaust chambers
-Fill the space on top of the oven with more sand
-Cover the top of the oven structure with something? Maybe just a lime cement render, maybe nothing at all...
-Extend the cabin roof over the oven

-(Some later date) enclose the oven in an all-weather room, complete with concrete floor

D L Bahler

I should note,

The original German plans I'm using as a basis use 2 sets of vertical steel plates on the outside of the oven to reinforce the walls against the spreading of the arches. Those plates are attached to their counterparts on the opposite side of the oven via long steel rods, one set passing above the oven and the other passing through the sand-filled area directly beneath the oven floor.

I plan to do it slightly differently. I'll have steel rods that pass above the oven, much the same.
Instead of a second set of rods below the oven floor, I intend to use large tapcon screws to anchor to the concrete pad

D L Bahler

Another Progress Update

Today I laid up more of the outside walls, and also framed the two openings for the main oven door (two openings, because it goes through two different walls)



 

Here you can see the support for the first opening in the oven chamber. I used two pieces of angle iron, one on either side of the wall. Later on I plan to weld a steel plate across them to tie them together so they can't fall out.



 

You can also see the three pieces of thin firebrick laid in the opening, mortared down to the brick wall. These will be at the same height as the front of the oven floor (the rear will be about 1 1/2" higher, about a 2% slope) Which will actually allow for about 2" of sand under the brick of the floor.



 

I then laid up the front wall of the outer structure, and supported the bricks above the opening the same way.
You'll notice that the angle iron on the inside wall is longer than that on the outside wall. There being no mortar between the bricks of the inner structure, it's necessary the steel be under all of the bricks on this section of the wall (4') so they all sit at the same height. On the other wall, the difference can be made up with the mortar so I didn't need (or want, because it makes a weaker joint) as long an iron.



  

 


I put a scratch coat of the cement from the mortar over the front angle iron to make it blend in to the brick a little better. I doubt it will stay very well (who knows though, anyone whose done brick or block on concrete work knows how hard it can be to get cement off of your metal tools a day or two later) but in the mean time, I think it looks better

 

  

  

  

  

 

The oven door will be attached to the angle iron above the opening and hinge upward. I'll probably tap some kind of locking mechanism into the brick on either side, but the basic design of the door is to use its own weight to keep it shut.
The hinge straps will bolt to the angle iron, with a heavy bolt that passes through both pieces of metal, and is secured with a locking nut on the inside.



  

  

  

 

thecfarm

Like the buiding progress.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Weekend_Sawyer

Very nice, I am watching with interest!
Imagine, Me a Tree Farmer.
Jon, Appalachian American Wannabe.

JRWoodchuck

What is the benefit of dry stacking the interior wall?
Home built bandsaw mill still trying find the owners manual!

D L Bahler

Dry stacking allows the brick to expand and contact freely with the drastic changes in temperature (like a 900 degree range of difference) without having to worry about eventual mortar failure and fracture.
I'd imagine even refractory mortar would have a different expansion coefficient than the bricks themselves, so these heating and cooling cycles would eventually cause the mortar to degrade and break down (not necessarily because it can't put up with the heat, but because the expanding and contracting bricks would eventually pull it apart)

It's pretty common practice to lay ovens, furnaces, etc. dry.

We're relying in this case on the outer walls to provide most of the necessary structural strength as far as lateral forces are concerned, so there's really no reason why the oven chamber should be mortared together.


JRWoodchuck

That makes sense. Do you ever see any issues with the sand pushing the bricks inward?
Home built bandsaw mill still trying find the owners manual!

D L Bahler

There's not really enough sand to do that here. All in all, there will be a bit under a ton of sand to fill the wall cavities and the floor. So that's spread out around two 6 foot walls and a 4 foot wall. I havent calculated, but I'd imagine there to be only a couple psi of force against the walls from the sand. What's more of a concern is that the bricks will be forced outward by the arches, especially as weight is applied on top of them. This same weight will also press down on the bricks in the walls and create more friction between them.

D L Bahler

Last night I laid out the arch template (don't have any pictures yet, sorry) To figure out how many bricks exactly it would take to build each arch, and how much each would have to be tapered to fit securely without using mortar. Turns out, each arch (there will be 9 arches total) will use 21 bricks (the number has to be odd, because you need to have a key at the top of an arch) and each brick will need to be tapered 3/16". TO do this, I will use a diamond grinding wheel to carefully shape each brick -all 189 of them- plus the 18 bricks that will sit on top of the walls to hold the arch bricks at the proper angle.

Tonight I laid most of the remainder of the outside walls up to the height of the cross ties. There's still a few bricks to lay on the back, but I'll worry about that later.

I need to be getting a ton of sand shortly. The walls need filled in before I can lay up the arches, or else there will be nothing to hold them together.



  

  

  

  

  

  

  

 

I had a fun experience yesterday on the way to a job. Some tire shops, it seems, can't be trusted to torque lug nuts tight enough on a ton truck. While driving down the high way, the truck began to vibrate badly. I was getting ready to pull off on a side road when the tire exploded. As you can see, 4 of the lug bolts sheared off and the rim is trashed (want you can't see is the back side. where the rim deformed upon impact with the road)


JRWoodchuck

I really appreciate you taking the time to answer my questions. On the to do list to build something like this someday in the fairly near future! Really enjoying your photos. Thanks again! That's a little scary on the tire....
Home built bandsaw mill still trying find the owners manual!

Ljohnsaw

How high will the inside of the oven be?  Where you have the all-thread, is that the height it will be in the final build?  Will that pass over the vaulted inner oven?  I believe you mentioned that you will coat the out side of the inner wall with mud (dirt, not mortar).  Still planning on doing that?  Looking pretty tight to get in there to do that now!
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

D L Bahler

After building up the floor, the inside walls will be 9 inches tall in the front, 7 1/2" in the back. The arch is 7" tall, so the high point of the oven chamber is 16"

The threaded rod sits just over the top of the arch bricks (so not through the baking chamber) You can see the approximate height of the baking chamber arches if you look at the end walls of the inner chamber.

There is 4 1/2' between the two walls, there's plenty of room to stick a hand in there to mud the walls, though I'm not sure if the vertical walls will get i, because they don't really need it. Heat loss is going to primarily be upward, so I think it's more important to seal the top of the oven.


Bruno of NH

I carry a torque wench in my one ton plow truck and check the wheels because i had a lot of problems with the wheels this year  :(
Lt 40 wide with 38hp gas and command controls , F350 4x4 dump and lot of contracting tools

D L Bahler

While laying in bed last night I had a revelation.

I was thinking about the infill between the walls, and realized that for this purpose, dirt is just as good as sand. I have lots of dirt, a whole pile from digging the foundation trenches. So I filled the walls up with dirt, and also filled up the floor cavity, being careful to make it even as I could, and to break up any clumps I encountered.

Using dirt in the floor instead of sand does mean I have to be a lot more careful when setting the floor bricks and later when setting the arches. I've got to put pieces of plywood over the bricks so I don't compact the dirt and push it around too much. But once that's all done, I would think it should be OK.



  

  

  

  

  

  

  

 

A couple things to point out:

Dirt moves around a lot more than sand when you're working with it, due to the much smaller particle size. So you've got to be real careful when working with the floor like this. But once the bricks are all in, it's pretty secure and stable. Time will tell if this was a good idea or not.

You can also pretty clearly see the slope of the floor in some of these pictures. I Put a 2% grade on the floor because my plans said to do so. I imagine a few things thi will do:
Encourage the heat and smoke to draft backward, while helping to heat the floor evenly from front to back
Aid in scooping out the ash
Aid in loading and unloading the oven

There is a row of bricks in the rear of the oven you may have noticed are stacked atop the floor on their sides. there are 19 rows of bricks from front to back, and about 3/4" space between the 19th row and the rear wall (a consequence of dry stacking bricks whose dimensions are designed to account for mortar joints) This is too big a gap to simply leave, but too small to be able to cut clean bricks to fit in the space very well. I decided to put these bricks in like this to cover the gap, because the back foot or so of the oven is dead space anyway. I figured this would help airflow somewhat, and also cut off what is normally the dead corner of an oven of this design, the rear bottom corner where there's not good airflow.

I'm considering grinding an angle on their faces to improve circulation in the rear a little more.

D L Bahler

I put up the first arch tonight. I experimented around a bit to determine exactly how I want to support the arches, etc.

The picture here are actually of an early trial. It worked well enough, but I decided I wanted a more secure means of support so I took it down and redid it.
I ended up placing a brick to bridge the gap between the arch feet and the outer walls, since none of the other methods seemed to be satisfactory in this case.

Also not seen here iss an important step when laying up dry arches that I forgot (my battery died so I don't have any pictures of the final arch) That is to rub the top of the arch with dirt (or in this case, dirt mixed with some sand) or mortar or whatever is handy to fill in the gaps and imperfections. (The other option is to be incredibly precise grinding the angles on your bricks, but that's VERY difficult. If you rub a little something over it all to fill in the gaps you have a little room for error)
If you don't do this, the arch will have a tendency to go lopsided or even collapse.

If it wasn't currently below freezing, I would have rubbed it over with mud instead, but that will have to wait until later. 



  

  

 

You can see the slip form I'm using to put the arches together. I'm taking advantage of the sloped floor. The two 2x4's rest on a sheet of plywood in the rear of the oven and on a 2x4 in the front (accounting for the 1 1/2" of difference in height) When I want to remove the form from under a completed arch, I knock out the support 2x4 in front which allows the arch support to fall down and be removed. THe first arch is the most difficult to do this way, since the 2x4's don't drop down any in the very rear.

A few notes on making the arches for those following with interest of making their own oven:

It's easiest to grind the angle on just one side of the brick. Then alternate each brick as you lay it in (so the angle ground sides butt up against each other, unground sides butt, etc). It's hard to keep 2 faces flat when you grind the bricks down like this (I'm using a diamond grinding wheel, it makes a lot of dust but is pretty slick.)
If you don't think you can do a good job grinding, you can just lay them in without grinding, and pack refractory mortar in the wedged opening. The disadvantage of this is you have to wait for the mortar to set before you can move on to the next arch.

Just to reiterate, when you lay an arch dry and before you remove the form, rub it with dirt or fine sand (or a mixture of both) a smear it over with a slip or mortar mixture of some kind to fill in gaps and imperfections. Unless you make a check gauge and carefully craft each individual brick there are going to be imperfections and inconsistencies (or if you're lucky, you could get your hands on some arch or wedge bricks and then this step is unnecessary). When the support is removed the arch will seek to balance its forces within itself. If imperfections are present, it will average them out meaning the arch will go lopsided, and it will be 'wobbly' which means it might fall apart eventually. If the imperfections are too bad, it will fall apart right away. So filling in the gaps thoroughly makes it stable.
If I remove the template and the arch moves AT ALL, then I'm going to take it apart and redo it.

You really only need (and want) a flat segmental arch for an oven. This arch has 7" of rise over a 49" width, it's based on a 48" radius circle. That's actually more rise than I need for stability, I could get by with like 3 inches of rise to support the structure if I wanted to, but I chose to build an oven with shorter walls and a higher arch mostly because it looks better (even though nobody but me will hardly ever see the arches once it's all done)
The taller you make an arch, the harder it is to support.
Actually wehn I was taking one of my trial arches apart, a brick or two removed it fell down and the tops of the remaining bridges wedged themselves together to form a very strong and stable arch that had maybe 1" or so of rise.

When assembling the arches, make sure to firmly seat each brick as you lay it in, otherwise the arch will shift when you remove the supports. I take my masonry hammer and tap each brick several times until it seems to be firmly seated on the brick below it. Also take care to align each brick in every other direction as you seat it. Once the key is in place, and especially once the form is removed, it is very hard to adjust and move anything.

For these arches, I'm trying to make my keys to where they will drop in about halfway, and then need tapped in with the hammer the rest of the way. This way any slack that's left in the arch is taken out. This also will lift the arch above the form a little bit, which in turn means the top edges are being forced open (or the bottom edges being forced together) aim for consistency in how much the key drops in before being driven and how much wedge they have in them, otherwise your arches will not line up with each other.

ChugiakTinkerer

This is a fascinating project.  Thanks so much for the many pictures and the detailed description.
Woodland Mills HM130

D L Bahler

 

  

 

Here are some pictures of the arch that I kept. You can see the support for the arch cleats, and the dirt and sand I smeared in the top

D L Bahler

It's been a little while since I've been able to get any work done on the oven, but the day I found some time to pick up another load of bricks and to get to work on a couple more arches. The first Arch I laid today needed to have the vent holes for the smoke cut into it, so I just ground release in a couple sets of mating bricks to form the smoke holes. Other than that it's just business as usual.

  

  

  

  

  

 

Ljohnsaw

I was starting to have withdrawal symptoms waiting for the next installment! :D

That is going to be a lot of force on those outside walls, when are you going to put the reinforcement rods in place?  Also, only those two little smoke holes?  Or will another arch have more?
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

D L Bahler

Putting in tie rods is the next step. Im just putting them in as I get to them, so they won't be in my way as I work through the oven body.

Regarding the smoke holes,

They're large enough for what I need, there won't be a tremendously large fire in there, no more than a couple pieces of wood at once and not much volume of smoke as you burn it hot an burn off the flammable gasses in the smoke.

D L Bahler

Also the dry arches don't put more force on the walls than they are able to withstand, at least in the short term. The force lands fairly low on the brick walls, and the sheer strength of the mortar, though not high, is enough. Also the construction does ensure that the thrust is distributed fairly well into the outside wall

D L Bahler

Early Monday morning, a bad storm (not on the forecast at all) rolled in and dumped several inches of rain. I hadn't bothered to cover the under-construction oven, as the weather was forecasted clear all weak. The rain washed the sand behind the arch support, allowing the arches to push them side and collapse. The suddenness of all of it allowed the arches to slide into outer wall with enough force to knock it over. SO progress has been delayed as I repair the outer wall of the structure.
From now on, I'll be sure to cover it even if no rain is in the forecast. IT is march in Indiana, after all.

The arches are particularly vulnerable  when under construction. There is not very much holding them up at this point, and add to that that arches of this type are somewhat unstable without any load upon them.

Czech_Made

Sorry to hear about your misfortune.

Fallguy

I was telling my future daughter in law about your project and she was very interested. Have you had time to get back on the project yet?

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